1. Field of the Invention
The present invention relates to an exposure apparatus and method, an optical disc drive for, and recording and/or reproducing method of, recording and/or reproducing information signal to and/or from a signal recording medium.
2. Description of the Related Art
Write or read of information signal to or from an optical disc is done by condensing a laser light to a predetermined spot diameter and projecting it to a signal recording layer of an optical recording medium.
For the irradiation of the laser light converged to the predetermined spot diameter to the signal recording surface layer, it is necessary to adjust the distance between an objective lens and optical disc for the signal recording layer of the optical disc to be positioned within a focal depth of the objective lens.
The above is also true with exposure of a photoresist coated applied on a disc-like substrate to a laser light to produce a stamper for use to manufacture of an optical disc. That is, it is necessary to converge the laser light to a predetermined spot diameter and project it to the photoresist on the glass substrate. The exposure on the disc-like substrate of the photoresist to the laser light is effected as will further be described below with reference to FIG. 1.
First, a disc-like substrate 101 having a smooth, mirror-finished surface is prepared as shown in FIG. 1. The substrate 101 is made of glass, for example.
As shown in FIG. 1B, the substrate 101 is applied to the smooth, mirror-finished surface thereof with a photoresist layer 102 to a predetermined thickness.
Then, a laser light is projected through an objective lens 112 to the photoresist layer 102 on the substrate 101 being rotated as shown in FIG. 1C. At this time, the objective lens 112 is moved in the direction of the optical axis thereof so that a laser light spot having a predetermined diameter will be defined on the photoresist layer 102. Namely, the laser light is focused on the photoresist layer 102.
Owing to this exposure to the laser light, there will be formed a fine latent image 102a, namely, latent image of a pit or groove, along a spiral line. Thus, the photoresist layer 102 will have a pattern of latent pit or groove images formed therein.
By developing the photoresist layer 102 thus exposed to the laser light, parts of the photoresist layer 102 on the substrate 101 are removed according to the exposed pattern as shown in FIG. 2, to provide an original substrate having tiny pits or grooves formed and which is used for further preparing a stamper for manufacture of an optical disc. The tiny concavities and convexities 102b in the photoresist layer 102 as shown in FIG. 2A will result in lands and grooves in the optical disc, while the tiny concavities and convexities 102c in the photoresist layer 102 as shown in FIG. 2B will result in pits in the optical disc.
The original substrate thus formed using the exposure apparatus is used to prepare a stamper for use to manufacture an optical disc.
As in the above, for the exposure apparatus used to prepare the original substrate for the optical disc stamper and optical disc drive to write or read information signal to or from the optical disc thus manufactured, a technique is required to irradiate a light sport having a predetermined diameter to an object such as an original substrate for manufacture of an optical disc and the optical disc itself. Conventionally, the astigmatic method, skew beam method, knife edge method, etc. are adopted to control the distance between the objective lens and object (will be referred to as xe2x80x9cgap lengthxe2x80x9d hereinafter). However, all these methods use a reflected laser light from the signal recording layer of the optical disc.
To meet the recent need for a higher density recording in the optical disc, it has been proposed to dispose between a condenser lens and optical disc a solid immersion lens (SIL) being a part cut from a spherical lens and having a high refractive index in order to further reduce the diameter of laser light spot which is defined on the photoresist on the original substrate or the optical disc. The condenser lens and SIL form together a so-called two-group lens. Owing to the SIL, a larger numerical aperture than that of the condenser lens (larger than 1 for example) can be realized. For example, the SIL is disposed on the optical disc so that the distance (namely, gap length) between the main side thereof (opposing the optical disc) and optical disc is on the order of 100 mn and thus within a so-called near-field area.
If the gap length between the SIL and an object (photoresist on the original substrate or optical disc) is outside the near-field area when the numerical aperture is larger than 1, a component of the intensity of the laser light outgoing from the SIL towards the optical disc, which causes the numeral aperture to be larger than 1, is considerably low. Therefore, it is necessary to control the gap length for the gap length to be constant inside the near-field area.
Even when the gap length between the SIL and object varies in a very narrow range such as the near-field area, the reflected laser light from the optical disc will vary very little. So, it is difficult to detect the gap length between the SIL and object with a high accuracy based on a variation of the reflected laser light from the optical disc. Therefore, with the conventional control of the gap length based on the reflected laser light from the optical disc, it is difficult to control the gap length between the SIL and object with a high accuracy.
Accordingly, the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing an exposure apparatus and method, and recording and/or reproducing apparatus and method, in which the gap length in the near-field area can be controlled with a high accuracy.
The above object can be attained by providing an exposure apparatus having a convergent lens disposed opposite to an object and in a near-field of the object to converge an exposure laser light on the object, the apparatus including according to the present invention:
an exposure light source to emit the exposure laser light;
a gap length controlling light source to emit a gap length controlling laser light different in wavelength from the exposure laser light;
means for projecting the gap length controlling laser light to the convergent lens;
means for detecting the intensity of a return part of the gap length controlling laser light from a surface of the convergent lens opposite to the object; and
means for controlling the gap length between the convergent lens and object based on the light intensity detected by the light intensity detecting means.
In the above exposure apparatus, the gap length controlling laser light different in wavelength from the exposure laser light is projected onto the convergent lens by the light projecting means, and the intensity of the return part of the gap length controlling laser light from the surface of the convergent lens opposite to the object is detected by the light intensity detecting means. Based on the return light intensity detected by the light intensity detecting means, the gap length between the convergent lens and object is controlled by the gap length controlling means.
Thus, in the exposure apparatus, the gap length between the convergent lens which condenses the exposure laser light on the object and the object is controlled based on the detected intensity of the return part of the gap length controlling laser light from the surface of the convergent lens opposite to the object.
Also the above object can be attained by providing an exposure method in which in which an exposure laser light is converged on an object by a convergent lens disposed opposite to the object and in a near-field area of the object, the method including, according to the present invention, steps of:
projecting a gap length controlling laser light having a different wavelength from that of the exposure laser light to the convergent lens upon which the exposure laser light is incident;
detecting the intensity of a return part of the gap length controlling laser light from a surface of the convergent lens opposite to the object; and
controlling the gap length between the convergent lens and object based on the detected intensity of the return light.
Thus, in the exposure method, the gap length between the convergent lens which condenses the exposure laser light on the object and the object is controlled based on the detected intensity of the return part of the gap length controlling laser light from the surface of the convergent lens opposite to the object.
Also the above object can be attained by providing an optical disc drive having a convergent lens disposed opposite to a signal recording medium object and in a near-field of the signal recording medium to converge a writing and/or reading laser light on the signal recording medium, the apparatus including according to the present invention:
a light source to emit the writing and/or reading laser light;
a gap length controlling light source to emit a gap length controlling laser light different in wavelength from the writing and/or reading laser light;
means for projecting the writing and/or reading laser light to the convergent lens;
means for detecting the intensity of a return part of the writing and/or reading laser light from a surface of the convergent lens opposite to the signal recording medium; and
means for controlling the gap length between the convergent lens and signal recording medium based on the light intensity detected by the light intensity detecting means.
In the above optical disc drive, the gap length controlling laser light different in wavelength from the writing and/or reading laser light is projected onto the convergent lens by the light projecting means, and the intensity of the return part of the gap length controlling laser light from the surface of the convergent lens opposite to the signal recording medium is detected by the light intensity detecting means. Based on the return light intensity detected by the light intensity detecting means, the gap length between the convergent lens and signal recording medium is controlled by the gap length controlling means.
Thus, in the optical disc drive, the gap length between the convergent lens which condenses the exposure laser light on the object and the object is controlled based on the detected intensity of the return part of the gap length controlling laser light from the surface of the convergent lens opposite to the object.
Also the above object can be attained by providing a recording and/or reproducing method in which in which a writing and/or reading laser light is converged on a signal recording medium by a convergent lens disposed opposite to the signal recording medium and in a near-field area of the signal recording medium, the method including, according to the present invention, steps of:
projecting a gap length controlling laser light different in wavelength from the writing and/or reading laser light to the convergent lens upon which the writing and/or reading laser light is incident;
detecting the intensity of a return part of the gap length controlling laser light from a surface of the convergent lens opposite to the signal recording medium; and
controlling the gap length between the convergent lens and signal recording medium based on the detected intensity of the return light.
Thus, in the recording and/or reproducing method, the gap length between the convergent lens which condenses the exposure laser light on the object and the object is controlled based on the detected intensity of the return part of the gap length controlling laser light from the surface of the convergent lens opposite to the object.